In the prior art, joining of piping materials is usually achieved by means of press rolls rotatively driven to caulk the joint of the piping materials where they are overlapped with each other. However, the joining of piping materials by use of such rotatively driven press rolls unfavorably requires a complicated structure, leading to an expensive and large-sized device to make the handling of the piping materials in the site of piping operation quite troublesome.
Thus, the present applicant previously proposed a device for joining piping materials without using press rolls in the Japanese Provisional Patent Publication (KOKAI) No. 109536/1982, which involves YOSEZUME (a plural number of dies movable in the radial direction) as the caulking means which can approach the piping materials in the orthogonal direction to the axis of the piping materials, but this device also suffers a problem of complicated cam mechanism for interlocking the YOSEZUME.
Furthermore, the present applicant proposed a device for joining piping materials in the Japanese Provisional Patent Publication (KOKAI) No. 142729/1982, in which a pair of dies are allowed to approach relative to each other in a direction parallel to the axis of the piping materials by use of cams which are movable in the orthogonal direction to the axis of the piping materials to achieve joining of the piping materials. Nevertheless, there remains a problem that the dies fail to keep their parallel face-to-face relationship because of the structure in which the dies are only pushed at their back portions by the cams to receive greater resistance from the piping materials at their portions facing to the piping materials to break the parallel relationship therebetween, whereby said portions are slightly opened or lifted up from the surface of the piping material as compared with the back portions thereof, so that the joining of a piping material and a pipe coupling cannot be achieved properly.